Power MOSFETs (Metal Oxide Semiconductor Field Effect Transistor) are examples of high breakdown voltage semiconductor devices which are used for switching power sources, inverter devices or the like. For example, power MOSFETs are considered to switch high voltages at low-ohmic load so as to have a very small switching and conduction loss. Vertical field-effect transistors (FET) in source-down structure are vertical FETs, in which drain and gate terminals are located on one side (top side) of a semiconductor substrate, while the source terminal is located on the other side (back side) of the semiconductor substrate. These FETs are useful in applications in which the source terminal of a semiconductor device is at a reference potential and in applications which require a good cooling. One possible application area for these semiconductor devices is in the automotive industry. Due to the source-down structure, energy may be efficiently dissipated which results in a further shrink of Ron. In these devices, it is desirable to lead potentials, which are different from the source potential, to the top side of the substrate.
Accordingly, it is desirable to develop new concepts of a semiconductor device. Further, it is desirable develop a new method for manufacturing such a semiconductor device.